There are numerous threads on the board that clearly address the issue of Job and birthdays.
Narkissos is correct (I'm sure he rests easy that I agree ).
When you really research the subject by studying the Hebrew text and reading various Bible commentaries you see that there is weak or no evidence that this scripture points to birthdays.
A few commentaries make the argument that birthdays are implied, but isn't that exactly what the WT does in so many cases (i.e. evidently, apparently, must be the case, etc etc).
I slay the birthday argument this way:
we celebrate anniversaries - we give anniversary gifts - who gets the gifts? God or the couple? In fact the longer a couple is married the more everyone discusses the couple and their ability to stay together and how proud of them everyone is. Hmmm. shouldn't all honor go to God?
we celebrate births - we give baby showers with gifts - who gets the gifts? God or the couple/baby?
Birthdays are not called out as bad in the Bible. From the above examples we see that we could celebrate birthdays by stating we are celebrating God's invention of the life giving process. We could give gifts to the individual because we are following the example set by the anniversary and baby shower routine.